Python Syntax

Python is known for its clean and readable syntax, which makes it an excellent language for beginners, but also powerful enough for advanced applications. In this article, we will learn about the basic elements of Python syntax.

Prerequisites: Before diving into Python syntax, ensure you have:

• Install Python (preferably Python 3.x).
• A text editor or IDE (Integrated Development Environment) like VSCode, PyCharm, or even IDLE (Python’s built-in IDE).

What is Python Syntax?

Python syntax refers to the set of rules that defines the combinations of symbols that are considered to be correctly structured programs in the Python language. These rules make sure that programs written in Python should be structured and formatted, ensuring that the Python interpreter can understand and execute them correctly. Here are some aspects of Python syntax: Along with this article you can also go through our Free Python Course to understand the concept of Python Syntax.

Running Basic Python Program

There are different ways of running Python programs. Below are some of the most widely used and common ways to run the Python program.

Python Hello World

This is the simple printing of hello world program in Python.

print("Hello, World!")

Output:

Hello, World!

Python Interactive Shell

1. Start the Python interpreter by simply typing python (or python3 on some systems) in the terminal or command prompt. We can then run Python commands interactively.
2. To exit, we can type exit() or press Ctrl + D.

Example of Python Interactive Shell

Running a Python Script

Create a script with the .py extension, e.g., Namaste.py.

Run it from the terminal or command prompt using: python script.py (or python Namaste.py).

Indentation in Python

Python Indentation refers to the use of whitespace (spaces or tabs) at the beginning of a line of code in Python. It is used to define the code blocks. Indentation is crucial in Python because, unlike many other programming languages that use braces “{}” to define blocks, Python uses indentation. It improves the readability of Python code, but on other hand it became difficult to rectify indentation errors. Even one extra or less space can leads to identation error.

if 10 > 5:
    print("This is true!")

if 10 > 5:
    print("This is true!")

Python Variables

Variables in Python are essentially named references pointing to objects in memory. Unlike some other languages, in Python, you don’t need to declare a variable’s type explicitly. Based on the value assigned, Python will dynamically determine the type. In the below example, we create a variable ‘a’ and initialize it with interger value so, type of ‘a’ is int then we store the string value in ‘a’ it become ‘str’ type. It is called dynamic typing which means variable’s data type can change during runtime.

Python Identifiers

In Python, identifiers are the building blocks of a program. Identifiers are unique names that are assigned to variables, functions, classes, and other entities. They are used to uniquely identify the entity within the program. They should start with a letter (a-z, A-Z) or an underscore “_” and can be followed by letters, numbers, or underscores. In the below example “first_name” is an identifier that store string value.

first_name = "Ram"

For naming of an identifier we have to follows some rules given below:

• Identifiers can be composed of alphabets (either uppercase or lowercase), numbers (0-9), and the underscore character (_). They shouldn’t include any special characters or spaces.
• The starting character of an identifier must be an alphabet or an underscore.
• Certain words in Python, known as keywords, have specific functions and meanings. These words can’t be chosen as identifiers. For instance, “for”, “while”, “if”, and “else” are keywords and cannot be used as identifiers. Even though “print” is not a keyword, it is a built-in function, so it should not be used as an identifier to avoid conflicts.
• Within a specific scope or namespace, each identifier should have a distinct name to avoid conflicts. However, different scopes can have identifiers with the same name without interference.

Python keywords

Keywords in Python are reserved words that have special meanings and serve specific purposes in the language syntax. They cannot be used as identifiers (names for variables, functions, classes, etc.). Below is the list of keywords in Python:

False       await         else          import          pass
None       break        except     in                   raise
True        class           finally      is                    return
and         continue    for           lambda         try
as            def             from        nonlocal       while
assert     del              global      not                with
async      elif              if              or                  yield

With different versions of Python some keywords may vary. We can see all the keywords of current version of Python using below code.

>>>import keyword
>>>print(keyword.kwlist)

Comments in Python

Comments in Python are statements written within the code. They are meant to explain, clarify, or give context about specific parts of the code. The purpose of comments is to explain the working of a code, they have no impact on the execution or outcome of a program.

Python Single Line Comment

Single line comments are preceded by the “#” symbol. Everything after this symbol on the same line is considered a comment and not considered as the part of execution of code. Below is the example of single line comment and we can see that there is no effect of comment on output.

first_name = "Reddy"
last_name = "Anna"

# print full name
print(first_name, last_name)

Reddy Anna

Python Multi-line Comment

Python doesn’t have a specific syntax for multi-line comments. However, programmers often use multiple single-line comments, one after the other, or sometimes triple quotes (either ”’ or “””), even though they’re technically string literals. Below is the example of multiline comment.

# This is a Python program
# to explain multiline comment.

'''
Functions to print table of
any number.
'''
def print_table(n):
  for i in range(1,11):
    print(i*n)
    
print_table(4)

4
8
12
16
20
24
28
32
36
40

Multiple Line Statements

Writing a long statement in a code is not feasible or readable. Writing a long single line statement in multiple lines by breaking it is more readable so, we have this feature in Python and we can break long statement into different ways such as:

Using Backslashes (\)

In Python, you can break a statement into multiple lines using the backslash (\). This method is useful, especially when we are working with strings or mathematical operations.

sentence = "This is a very long sentence that we want to " \
           "split over multiple lines for better readability."

print(sentence)

# For mathematical operations
total = 1 + 2 + 3 + \
        4 + 5 + 6 + \
        7 + 8 + 9

print(total)

This is a very long sentence that we want to split over multiple lines for better readability.
45

Using Parentheses

For certain constructs, like lists, tuples, or function arguments, we can split statements over multiple lines inside the parentheses, without needing backslashes.

# Create list
numbers = [1, 2, 3,
           4, 5, 6,
           7, 8, 9]

def total(num1, num2, num3, num4):
  print(num1+num2+num3+num4)
  
# Function call
total(23, 34,
      22, 21)

100

Triple Quotes for Strings

If we are working with docstrings or multiline strings, we can use triple quotes (single ”’ or double “””).

text = """GeeksforGeeks Interactive Live and Self-Paced
Courses to help you enhance your programming.
Practice problems and learn with live and online
recorded classes with GFG courses. Offline Programs."""

print(text)

GeeksforGeeks Interactive Live and Self-Paced
Courses to help you enhance your programming.
Practice problems and learn with live and online
recorded classes with GFG courses. Offline Programs.

Quotation in Python

In Python, strings can be enclosed using single (‘), double (“), or triple (”’ or “””) quotes. Single and double quotes are interchangeable for defining simple strings, while triple quotes allow for the creation of multiline strings. That we have used in above example. The choice of quotation type can simplify inserting one type of quote within a string without the need for escaping, for example, using double quotes to enclose a string that contains a single quote. Below is the example of using single and double quotes.

# Embedded single quote inside double.
text1 = "He said, 'I learned Python from GeeksforGeeks'"

# Embedded double quote inside single.
text2 = 'He said, "I have created a project using Python"'

print(text1)
print(text2)

He said, 'I learned Python from GeeksforGeeks'
He said, "I have created a project using Python"

Continuation of Statements in Python

In Python, statements are typically written on a single line. However, there are scenarios where writing a statement on multiple lines can improve readability or is required due to the length of the statement. This continuation of statements over multiple lines is supported in Python in various ways:

Implicit Continuation

Python implicitly supports line continuation within parentheses (), square brackets [], and curly braces {}. This is often used in defining multi-line lists, tuples, dictionaries, or function arguments.

# Line continuation within square brackets '[]'
numbers = [
    1, 2, 3,
    4, 5, 6,
    7, 8, 9
]

# Line continuation within parentheses '()'
result = max(
    10, 20,
    30, 40
)

# Line continuation within curly braces '{}'
dictionary = {
    "name": "Alice",
    "age": 25,
    "address": "123 Wonderland"
}

print(numbers)
print(result)
print(dictionary)

[1, 2, 3, 4, 5, 6, 7, 8, 9]
40
{'name': 'Alice', 'age': 25, 'address': '123 Wonderland'}

Explicit Continuation

If you’re not inside any of the above constructs, you can use the backslash ‘\’ to indicate that a statement should continue on the next line. This is known as explicit line continuation.

# Explicit continuation
s = "GFG is computer science portal " \
    "that is used by geeks."

print(s)

GFG is computer science portal that that is used by geeks.

Note: Using a backslash does have some pitfalls, such as if there’s a space after the backslash, it will result in a syntax error.

Strings

Strings can be continued over multiple lines using triple quotes (”’ or “””). Additionally, if two string literals are adjacent to each other, Python will automatically concatenate them.

text = '''A Geek can help other
Geek by writing article on GFG'''

message = "Hello, " "Geeks!"

print(text)
print(message)

A Geek can help other
Geek by writing article on GFG
Hello, Geeks!

String Literals in Python

String literals in Python are sequences of characters used to represent textual data. Here’s a detailed look at string literals in Python. String literals can be enclosed in single quotes (‘), double quotes (“), or triple quotes (”’ or “””).

string1 = 'Hello, Geeks'
string2 = "Namaste, Geeks"

multi_line_string = '''Ram learned Python
by reading tutorial on
GeeksforGeeks'''

print(string1)
print(string2)
print(multi_line_string)

Hello, Geeks
Namaste, Geeks
Ram learned Python
by reading tutorial on
GeeksforGeeks

Command Line Arguments

In Python, command-line arguments are used to provide inputs to a script at runtime from the command line. In other words, command line arguments are the arguments that are given after the name of program in the command line shell of operating system. Using Python we can deal with these type of argument in various ways. Below are the most common ways:

• Using sys.argv
• Using getopt module
• Using argparse module

Example: In this example we write the program to sum up all the numbers provided in command line. Firstly we import sys module. After that we checks if there are any numbers passed as arguments. Iterates over the command-line arguments, skipping the script name i.e. “sys.argv[0]” and then converts each argument to a float and then add them. We have used try-except block to handle the “ValueError”.

import sys

# Check if at least one number is provided
if len(sys.argv) < 2:
    print("Please provide numbers as arguments to sum.")
    sys.exit(1)  # Exit with an error status code

try:
    # Convert arguments to floats and sum them
    total = sum(map(float, sys.argv[1:]))
    print(f"Sum: {total}")
except ValueError:
    print("All arguments must be valid numbers.")

Please provide numbers as arguments to sum.

Output: In the output we can see that the program returns the total of numbers passed as an arguments.

Taking Input from User in Python

The input() function in Python is used to take user input from the console. The program execution halts until the user provides input and presses “Enter”. The entered data is then returned as a string. We can also provide an optional prompt as an argument to guide the user on what to input.

Example: In this example, the user will see the message “Please enter your name: “. After entering their name and pressing “Enter”, they’ll receive a greeting with the name they provided.

# Taking input from the user
name = input("Please enter your name: ")

# Print the input
print(f"Hello, {name}!")

Output:

Please enter your name:
Sagar
Hello, Sagar!

sagar99

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